1. Field of the Invention
The present invention relates to a deposited film forming apparatus (a plasma CVD apparatus etc.) and a deposited film forming method for forming a deposited film, particularly a functional deposited film (for example, an amorphous semiconductor used for semiconductor devices, electrophotographic photosensitive members, photovoltaic devices, and so on) or the like, on a substrate.
2. Related Background Art
Suggested as device materials used for the semiconductor devices, electrophotographic photosensitive members, photovoltaic devices, and various other electronic devices are non-monocrystalline deposited films such as amorphous silicon, for example, typified by amorphous silicon compensated by hydrogen or/and halogen (for example, fluorine, chlorine, etc.) (which will hereinafter be abbreviated as “a—Si:H,X”), or crystalline deposited films such as thin films of diamond, and some of them are used in practice. These deposited films are formed, for example, by the plasma CVD method, i.e., by a method for decomposing a source gas by a glow discharge induced by direct current, high-frequency wave, or microwave and forming a deposited film on such a substrate as glass, quartz, a heat-resistant synthetic resin film, stainless steel, or aluminum, and a variety of devices for carrying out the method are also suggested.
An example of such a forming apparatus and forming method of deposited film is one briefly described below.
FIG. 1A and FIG. 1B are schematic structural diagrams to show an example of an apparatus for producing an electrophotographic photosensitive member by the high-frequency plasma CVD method. The structure of the production apparatus illustrated in FIGS. 1A and 1B is as follows.
This apparatus is generally composed of a deposition system 1100, a source gas supply system 1200, and an exhaust system (not illustrated) for reducing the pressure inside a reaction vessel 1111. Inside the reaction vessel 1111 in the deposition system 1100 there are cylindrical substrates 1112, heaters 1114 for heating the respective substrates, source gas inlet pipes 1115, and a cathode electrode 1116, and a high-frequency power supply 1117 and a high-frequency matching box 1118 are connected to the cathode electrode 1116.
The source gas supply system 1200 has cylinders 1221 to 1226 for supplying respective source gases of SiH4, GeH4, H2, CH4, B2H6, PH3, etc., valves 1231 to 1236, and mass flow controllers 1211 to 1216, and the cylinder of each source gas is connected via an auxiliary valve 1260 to the gas inlet pipes 1115 in the reaction vessel 1111.
Formation of a deposited film using the deposited film forming apparatus described above is carried out, for example, as described below.
First, cylindrical substrates 1112 as substrates for forming the deposited film thereon are set in the reaction vessel 1111 by use of substrate holding means 1113 and the inside of the reaction vessel 1111 is evacuated by the unrepresented exhaust device (for example, a vacuum pump). Subsequently, the temperature of the cylindrical substrates 1112 is set to a predetermined temperature in the range of 200 to 450° C. by the heaters 1114 for heating the respective substrates.
For letting the source gases for formation of the deposited film into the reaction vessel 1111, after confirming that the valves 1231 to 1236 of the gas cylinders are closed and that the inflow valves 1241 to 1246, outflow valves 1251 to 1256, and auxiliary valve 1260 are opened, an exhaust valve (not illustrated) is first opened to evacuate the inside of the reaction vessel 1111 and the gas pipe 1119.
When the vacuum gauge (not illustrated) reaches about 6.7×10−4 Pa, the auxiliary valve 1260 and outflow valves 1251 to 1256 are closed. Thereafter, the cylinder valve 1231 to 1236 are opened to introduce each gas from the corresponding gas cylinder 1221 to 1226 and the pressure of each gas is adjusted to about 2 kg/cm2 by pressure regulator 1261 to 1266. Then the inflow valve 1241 to 1246 are gradually opened to introduce each gas into the mass flow controller 1211 to 1216.
After completion of the preparation for film formation as described above, formation of each layer is carried out according to the following procedures. When the cylindrical substrates 1112 reach a predetermined temperature, necessary valves out of the outflow valves 1251 to 1256, and the auxiliary valve 1260 are gradually opened to introduce predetermined gases from the corresponding gas cylinders 1221 to 1226 through the gas inlet pipe 1115 into the reaction vessel 1111. Then each source gas is adjusted to a predetermined flow rate by the corresponding mass flow controller 1211 to 1216. On that occasion, the aperture of the exhaust valve (not illustrated) is adjusted with observing the vacuum gauge (not illustrated) so that the pressure inside the reaction vessel 1111 is not more than 1.3×102 Pa. When the internal pressure becomes stable, the high-frequency power supply 1117, for example, of the frequency 13.56 MHz is set to a desired power and the high-frequency power is supplied via the high-frequency matching box 1118 and cathode electrode 1116 into the reaction vessel 1111, thereby inducing the glow discharge. The source gases introduced into the reaction vessel 1111 are decomposed by this discharge energy to form a predetermined deposited film having the matrix of silicon on the cylindrical substrates 1112. After the film is formed in a desired thickness, the supply of the high-frequency power is stopped and the outflow valves are closed to stop the flow of the gases into the reaction vessel 1111, thereby completing the formation of the deposited film.
A photosensitive layer can be formed in a multilayer structure by repeating the above-described operation.
Multiple layers may be formed continuously to gradually change the high-frequency power, gas flow rates, and pressure to their set values for the next layer in a fixed time after completion of formation of one layer.
It is needless to mention that all the outflow valves other than those for necessary gases are closed during the formation of each layer. In addition, an operation for closing the outflow valves 1251 to 1256, opening the auxiliary valve 1260, and fully opening the exhaust valve (not illustrated) to evacuate the inside of the system once to a high vacuum is carried out as needed in order to prevent the gases from remaining inside the reaction vessel 1111 and inside the pipe from the outflow valves 1251 to 1256 to the reaction vessel 1111. During the formation of the deposited film, a motor 1120 is driven to rotate a rotational shaft 1122 via gears 1121 and in turn rotate each cylindrical substrate 1112, whereby the deposited film is formed throughout the entire circumference of the surface of each cylindrical substrate 1112.
Although good a-Si base electrophotographic photosensitive members are formed by the above-stated apparatus and method, the above apparatus and method require further improvement in order to enhance the overall characteristics.
Particularly, the increase in the speed of the electrophotographic apparatus is advancing rapidly and there are demands for further enhancement of electrical characteristics of the electrophotographic photosensitive members.
As the performance of the main body of copiers is rapidly improving and as digital copiers and color copiers have spread in recent years, the electrophotographic photosensitive members are required to implement further enhancement of image characteristics such as higher quality of image or higher quality of product than heretofore.
Further, as the size of copying machines is decreasing and as the demand for light receiving members such as printers is increasing, the demand for the electrophotographic photosensitive members of smaller diameters is also increasing. Development is needed of a production apparatus that can adapt to the decrease in size.
Under such circumstances, the technology that allows to maintain the uniformity of plasma, long-term stability, and uniformity of film thickness and film quality with good repeatability is strongly demanded in the field of producing electrophotographic photosensitive members in order to achieve the above needs.
Further, it also becomes necessary to eliminate small image defects which were insignificant heretofore. The principal cause of the image defects is in that the deposited film peels off and scatters onto the substrate resulting in abnormal growth. It is thus necessary to prevent pieces of the film, which will cause image defects, from peeling onto the substrate.